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PIERS MORGAN, CNN ANCHOR: This is PIERS MORGAN LIVE. Want to welcome our viewers in the United States and around the world to CNN's team coverage of terror at the Boston Marathon. Millions are stunned tonight by what appears to be a coordinated terror attack by one of the world's elite and most popular athletic events.

Two bombs near the finishing line blowing up within 12 seconds of each other and ripping through crowd of spectators about two hours after the elite runners have passed through. This is new video of the second explosion showing how deadly it was.

Here's what we know right now. The toll of injuries are still rising, at least 144 people are being treated right now in Boston hospitals. Three are dead. One of the victims is an 8-year-old boy. Limbs are being amputated.

Doctors are reportedly pulling ball bearings out of victims. A law enforcement source in Boston tells CNN there are a number of active leads, but no identified suspects. A man with a black backpack and black sweatshirt reportedly tried to get into a restricted area.

This is the instant that thousands of people went running for the finishing line to running for their lives. The whole thing captured in this shocking video.

Devastating scenes there in Boston. I want to bring Chris Cuomo now who is live in Boston tonight. Chris, we're getting nearer to having any idea who may have caused the atrocity?

CHRIS CUOMO, CNN CORRESPONDENT: Well, we do know that there are advances in the investigation, Piers and that's not to be coy. It's very early here. This is a very difficult scenario to pick up on --

MORGAN: So we're going to talk to Jason instead who is at Brigham and Women's Hospital. Jason, I believe 31 patients are being treated there. Two of those, obviously, are very critical tonight. Nine have gone to the operating triage. What are you expecting to have happen in the next few hours there?

JASON CARROLL, CNN NATIONAL CORRESPONDENT: It is going to be a lot of hard work for the surgeons who are here, Piers. There is just no other way to say it. You when I was standing out here, one of the attendants came out and said in the very beginning, Piers, the ambulances were coming in droves, six at a time. Another nurse coming out here and basically saying no matter what type of training everyone here has received and you know, they drill for things like this. But all lof the training in the world, nothing could have prepared them for what they are dealing with inside right now.

I spoke to one of the doctors here, Dr. Ron Walls. He very much described the injuries, the extensive injuries that the patients here are suffering with, most of the injuries to the lower extremities. There are two people in critical condition fighting for their lives at this very moment.

I want you to listen to what Dr. Walls how he described the injuries that they're facing.

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RON WALLS, MD, EMERGENCY MEDICINE PHYSICIAN: The worst of these injuries have been injuries to the legs. There have been a lot of damage such as a lot of blast effect from these types of explosions. So a lot of injury to the muscle, the skin and the bones are broken, those sorts of injuries. The shrapnel injuries have been ambient things thrown around in the blast.

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CARROLL: Nine of the patients that are here, nine of the 31 are being operated on at this hour. Two of those patients, Piers, we're being told, are in danger of losing their limb. That gives you another idea of what I'm telling you, the extent of the injuries that these people are dealing with. It's just horrific.

Again, one nurse who came outside said this has been an emotionally traumatizing type of day. The people here at this hospital are trained for this and it's just going to be a matter of a lot of hard work to save the lives of people who are still struggling to stave alive.

MORGAN: Jason, thank you so much. We will go back to Chris Cuomo live in Boston. We lost you there briefly. Bring us up to speed on where you feel the investigation may be going.

CUOMO: Right. We do have reason to believe, Piers, that they are making advances in this. This is a very difficult situation because there are so many people. There is much territory. There are so many different aspects of this investigation to pick on.

We do know that there are various federal state and local authorities coordinating this. There is a six-block perimeter they are going through it very carefully. They have understandings about the bombs. They are learning things from what they call the bomb signature.

They also know, Piers, that whoever did this knew the right place and the right time to be here at the marathon. Just before four hours and 10 minutes. That's when the thickest bunch of people are finishing the marathon and the area, the corner that was picked for this explosion was like the Times Square of the Boston marathon.

It's the most densely populated. So that takes specific knowledge. On the general side, they now understand a lot more about the explosives that were used. They were not high explosives that can have a blast rate of 20,000 feet per second, very powerful, waves that can damage and kill.

They believe this was black powder, less sophisticated, about 7,000 square feet per second, may have had ordinance in it, ball bearings and maybe things that picked up from surrounding buildings. Remember this for context, 7,000 feet per second, a handgun bullet coming out of a 9-mm is going about 1,000 or 1,200, very powerful.

You get hit from something that's blasted by this bomb it will create the kinds of terrible injuries that we saw today. In terms of specific suspects, people of interest, we're not hearing about any of that yet. There's good reason. The crime scene itself is still in very early stages here and under careful watch.

Because of all the different things that the federal authorities have to look at, backpacks and bags and all kinds of things that were left, because of what they know about the types of explosives here, those could have been potential.

There was reporting about them having suspicious packages, could be devices. Most of them looked clear. They used water cannon to do it. They have a lot of manpower on the ground. They're looking at cell tower information to try to piccolo occasion and different communication rates.

They're using CCTV, closed circuit TV. They're asking media outlets. They're looking at this very carefully, but it is a very big task.

MORGAN: There have been conflicting reports all day, Chris, particularly about possible undetonated devices. You touched on this just now. It was reported that maybe up to three bombs had not gone off, but that now seems to be unlikely?

CUOMO: You have to understand the protocol. When they come in, they are looking at suspicious packages. They are getting word of mouth about it. They could look like something that is recognizable from what they saw at the scene, so they treat it like a device that needs to be dismantled.

They believe they had as many as six of those today. There may have been a third. The good news is they don't believe at this time they have unexploded ordinants (ph) that they are trying to find. They are searching at hotels. They have locked down the area. So far there is no more bad news.

MORGAN: Chris, we've got the front page of the "Boston Globe" tonight, a very dramatic front page as you would imagine. It was a really powerful image there. You'd being on the ground a few hours now in Boston, how would you describe the mood there amongst the people of Boston? CUOMO: Well, we have people tonight tell us, you know, you always have pride in your hometown. Boston people are hard nose. No question about it. The stories that we have heard today of people who turned in the face of danger to help others. Because I'm telling you, Piers, we have not been showing the photos, but the injuries?

The fact that we have not heard about more lives lost is amazing to me looking at the injuries that I saw here today. People were coming together. There is shock in a situation like this. You have to remember the juxtaposition. This is a beautiful day here in Boston.

The marathon is a center of their culture, their heart. Patriot Day, they're here for all the best reasons and the worst things happen. Let alone the fact that so many people involved literally tens of thousands were under great stress running a marathon.

A lot to overcome here, a lot of the city in this area is lockdown, a lot of people stay here, but people have perspective. They understand that it could have been worse and they're bonding together.

As you know well, Piers, when we see these situations and we have had to cover too many. In the face of the worst you see the best in people and I believe that holds true here in Boston today.

MORGAN: People with great spirit in Boston and I'm sure they will rise to this extremely traumatic challenge. Chris, for now, thank you. We'll come back to you. The victims of Boston Marathon bombing have had horrific injuries including amputations and shrapnel damage.

We go now to CNN's chief medical correspondent Sanjay Gupta. Sanjay, it seems almost miraculous that at the moment the death toll is only at three people. Terrible for those who lost their lives, but given the scale of some of these injuries, are you surprised that figure is not a lot higher?

DR. SANJAY GUPTA, CNN CHIEF MEDICAL CORRESPONDENT: I am a bit surprised, but keep in mind a couple of things, Piers. One is that near the end of the race there is often a lot of medical capabilities sort of standing by, ambulances, expecting to treat things from dehydration to maybe heart issues.

This is obviously very different. For them they were able to take care of these patients pretty quickly and get them to nine different hospitals quickly in the city of Boston. So that certainly helped. I also think the nurses who were expecting to do triage at the end of the race just standing by there as well that probably helped a lot.

So we don't know the magnitude in terms of force of these explosive devices. It appears to have been a low sort of force. That's why so many lower extremity injuries as opposed to an upward and outward sort of forces.

And that may have played a role here as well, but some of the images that Chris was talking about, some of the things that he has seen, I think we, in some ways are lucky, Piers. MORGAN: Sanjay, in terms of what we are beginning to find out about the type of device that was used, many saying there was shrapnel-like wounds possibly from ball bearings. None of this is being completely confirmed yet, but with the type of injuries that we're seeing be consistent with that kind of device?

GUPTA: Yes, they would, Piers. What I specifically heard from the doctors earlier, when they were talking about these particular lower extremity injuries, they described bone injuries, but also soft tissue injuries and vascular or blood vessel injuries.

When you have an explosion like this, you certainly have a primary blast, which is a wave, if you will. After that, the secondary blast is typically made up of shrapnel. Often it's debris that is in the area.

Sometimes it can be things within the explosion itself whether they be ball bearings or something else and that would be consistent with these types of injuries especially to the soft tissue types of injuries that we saw, Piers.

MORGAN: Sanjay, for now thank you very much indeed. I'm going to go now to Paul Cruickshank, CNN contributor and terrorism analyst. Paul, really, I guess we don't know who has done this. That is the only fact that we do have about what maybe behind it. How soon do you think the FBI will be in a position when they have a lot more information?

PAUL CRUICKSHANK, CNN CONTRIBUTOR: Well, they are throwing huge amount resources at it. If you remember three years ago, there was attempted bombing in Times Square, New York. Actually an American recruiter, the Pakistani Taliban, well, it took them around 48 hours to make an arrest as he was trying to leave country to go to Dubai. So these things can be incredibly fast moving.

MORGAN: Hold it. We have breaking news from Brian Todd. He's on the ground. Police are surrounding a property in Revere on the outskirts of Boston. Brian, can you bring us up to speed on what is going on?

BRIAN TODD, CNN CORRESPONDENT (via telephone): Yes, Piers, we are at an apartment building on Ocean Avenue in the town of Revere, Massachusetts. It's just north east of Boston, a couple of miles northeast.

State police are here checking out an apartment. We got to the lobby of the building and spoke off camera with a couple of state police officials who confirmed they were checking out one apartment.

We asked for some more information and they would not give it but one of their superiors said all the questions have to go to the FBI and they shooed us out of the lobby. But we do know that state police have been here for some hours checking out some kind of a lead at an apartment here in Revere, Massachusetts.

One of the neighbors, a young lady told us that the authorities had been on site here at least since 5:30 p.m. and that she and her family were worried and scared by the presence of the law enforcement officers.

Now whether this is a solid lead in the investigation, we just don't know. But we do know, Piers, that state police are checking out an apartment on Ocean Avenue here in Revere, Massachusetts.

MORGAN: What I had read just before I came on air, Brian, which I think maybe connected was that the police had detected somebody behaving erratically I think in a car going through several roadblocks, and they had followed this person back. Is that anything you have heard?

TODD: We had not heard that. We'll certainly follow that if we can get some kind of -- some kind of word into the state police who are in the lobby, who now are not letting us in. But there are a lot of neighbors going around with some concern telling us that they've seen the police here for several hours now. The police would only tell us before they told us to get out of the building that they are checking out one apartment and possibly interviewing one of the residents.

MORGAN: Brian, for now, thank you. We'll come back to you if there's any more development on that breaking news there. Paul Cruickshank, in the hunt for whoever this is, most people believe if it wasn't al Qaeda related operation, they will probably claim some kind of credit. Is that your belief?

CRUICKSHANK: Well, that's right. But sometimes it takes them several months to claim credit if it is an al Qaeda related group. Sometimes, 48 hours so it really depends on attack to attack. So obviously a lot of people looking at all these Jihadi forums, but maybe an individual or completely unrelated to Islamists --

MORGAN: Has it got the hallmark of an al Qaeda operation in the sense of clearly has been some planning here. Some of the police believe that they much have been watching for when they did the sweep and then whoever it was put the devices specifically where they put them. That could be, you know, a crazy American. We don't know who this is, do we? It could be anybody.

CRUICKSHANK: That's right. It could certainly be a lone wolf or a group of individuals. Around a year ago, al Qaeda in the Arabian Peninsula, the Yemeni affiliate have released an article in their online English magazine calling for attacks on sporting venues and crowded places. They have calling for this sort of attack, but that doesn't mean that al Qaeda was responsible.

MORGAN: It's the anniversary of Patriots Day and tax day this week and so lots of potential reasons people are putting up for --

CRUICKSHANK: And the anniversary of the Bin Laden raid as well coming up, yes.

MORGAN: Right, that would lend more to perhaps an al Qaeda thing, but the others could lend its a domestic terror attack theory. What will the FBI be really pushing now? Chris Cuomo talked earlier, CCTV footage, I'm sure there will be a lot of that. The cell phone I guess will be extremely relevant and they can trace any calls particular linked to people they can see moving around certain areas.

CRUICKSHANK: Absolutely. And the forensics will be crucial as well. If they have recovered an intact device and the forensic is going to be much, much easier. If they do the forensics on the exploded devices, it's going to take a little bit more time to figure what sort of bomb was involved.

And if they do the forensics and they see it has a signature related to a track record of a group perhaps like al Qaeda or right wing extremist group or whatever, they can gain a huge amount of clues on who may have been responsible.

MORGAN: The president didn't use the word terror or terrorism when he spoke, which I found a little surprising given whatever this is. It's clearly an appalling act of terror by somebody.

CRUICKSHANK: Well, that's absolutely right. I mean, clearly they're being very cautious. They don't get ahead of --

MORGAN: Too cautious do you think?

CRUICKSHANK: I wouldn't want to weigh in on that, but clearly, caution is valuable here that being attacks in the past where different groups have been blamed and they've ended up not being responsible so cautious approach is probably the right approach.

MORGAN: The FBI has taken full control of the investigation. If it looks like it may be an Islamic fundamentalist group involved in some way, does the CIA then come in with them? How does it work?

CRUICKSHANK: Well, they certainly would if it's a foreign overseas aspect. If it's related to an overseas group, related to al Qaeda, for example, and then, you know, the full weight of the U.S. government in terms of the intelligence services would be and their partners overseas would be looking at that.

MORGAN: If it is al Qaeda, it will be a huge blow to the American war on terror after quite a long period without a major attack. I mean, this is the worst attack by a terror group or person since 9/11.

CRUICKSHANK: Well, it's still a very, very big if. There have been several dozen plots on the United States. Most of them have been home grown plots inspired by al Qaeda's ideology. In the last year or so that has tailed off a little bit. There haven't been quite as much activity, but it is related al Qaeda. Clearly it would be a success for them, but still a very, very big if at this point.

MORGAN: We'll stay with David. Take a short break. When we come back former Summer Sanders who crossed the finishing line just before the first explosion.

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CARLOS ARREDONDO, HELPED WOUNDED VICTIMS AFTER EXPLOSIONS: This big explosion took place in front of me and then I saw this cloud of smoke and my first instinct was to run across the street and start helping out the people.

UNIDENTIFIED MALE: Your sleeve there, is that blood?

ARREDONDO: On my pants and clothes.

UNIDENTIFIED MALE: Show me that flag?

ARREDONDO: That was a flag I was holding the whole time.

(END VIDEO CLIP)

MORGAN: One of the most dramatic stories of sudden terror. Joining me on the phone is former Olympic athlete, Summer Sanders, who finished the marathon before the first blast occurred. Summer, a terrifying day for so many the people involved in the marathon, tell me what happened to you.

SUMMER SANDERS, FORMER OLYMPIC SWIMMER RAN IN MARATHON (via telephone): Terrifying is -- it's putting it mildly. I finished it. The clock actually reads 3:37. I went into the medical tent and I remember saying to myself, my gosh, they are really set up for a lot of people in here. It was so smooth and they had it all down.

I walked back to my hotel and by the time I got up into my room that's when I heard the first blast. It completely freaked us out and then 20 seconds later, we heard a bigger more powerful blast that made me scream.

My first instinct was to get down to the lobby and get out. That's when the police blocked it off. We were on lock down for about 20 minutes and then it was police running through our halls, knocking on the doors saying everybody out, immediately evacuate.

MORGAN: You watch as a commentator for the Atlanta Olympics in 1996. Did images of what happened today bring flash backs to you?

SANDERS: Absolutely. I remember thinking of Janet Evans. She was doing an interview and I forget who it was for. I'll never forget her reaction when that bomb went off exactly what I thought of was that image and such a beautiful competition.

It's all about peace and play and sportsmanship and all of that. And this morning, you know, I was walking down the street in front of the buildings and it was a magical day. It was a day I looked forward to.

All of my fellow competitors have look forward to it, 27,400 or so of us, Piers and when you're a part of something like this, you're a family. Runners are -- we're a close knit group. If something like this happens, it affects every single one of us.

My heart is aching for everyone involved. Anyone who is affected by this or injured or has a family member, my heart is aching for them and thinking of them.

MORGAN: Yes, you speak for so many people and someone is glad that you made through OK and thank you very much for joining me.

SANDERS: Thanks, Piers.

MORGAN: I want to bring in Brittany Williams. She was running the marathon and had some terrifying moments when she was separated from her family waiting at the finishing line. She joins me now on the phone. Brittany, you were at the 25.7 mile marker when all of a sudden the police stopped the race. What was going through your mind?

BRITTANY WILLIAMS, RUNNER (via telephone): I just basically was confused. I thought that everyone -- I initially thought that everyone got lost. It was crazy because it's the Boston Marathon. You don't ever see any stopping. It was just massive confusion.

MORGAN: You had not heard any of the explosions?

WILLIAMS: I had my headphones in? I was listening to them louder. Someone had pointed out smoke, but we thought maybe there were fireworks or something going on at the finish line. Your initial thought when you're running a race is the competition and an event that is supposed to be fun that it would be a bomb going off.

MORGAN: Your parents, your grandmother, your brother, your boyfriend and your best friend, were all at the finishing line waiting for you. Once you realize what had happened, your heart must have sank. You must have feared something awful may have happened to one of them.

WILLIAMS: It was surreal. It was such a large group and we were right in the middle of it. But luckily, when I really kind of realize what was going on, I had already gotten in touch with them. I didn't realize the severity.

MORGAN: Britney, it's awful day for you and for everyone involved in the Boston marathon. Thank you for joining me. I'm just glad that you made it through OK.

WILLIAMS: Thank you very much.

MORGAN: Chris Cuomo is live for us again in Boston. He is with Marlo Fogelman who was at the marathon celebration close to finishing the line, a celebration that went horribly wrong -- Chris.

CUOMO: Piers, you have two types of people who experience this event. People who were too far away to figure out what it was and then people who were all too close. Marlo, you were just showing me photos on your Blackberry. They look directly down at the scene of the explosion and the aftermath of all those injuries. What was going on? You have a PR marketing company. You are having your party. What happens?

MARLO FOGELMAN, OWNER, MARLO MARKETING COMMUNICATIONS: We heard the explosions, two, right after each other. And I was in the back of the office. Everybody started running towards the back and away from the windows and noise. At first, we didn't know what to do.

CUOMO: You knew it was not part of the ceremony or fireworks with the first one, the second one?

FOGELMAN: This is the sixth year we have done this party and we have never had anything like this before. Again, it's just one of those things that you don't know what it is.

CUOMO: This is what we have been seeing all day. It is literally the building right behind the white building where the bomb went off. Did you feel as well as hear the explosion?

FOGELMAN: We didn't really feel it. We heard it. It was loud and we heard the other one that was further away. There was not enough of an impact to feel it in the building.

CUOMO: But you were close enough you say that smoke was coming up into your building, your floor where you were?

FOGELMAN: Absolutely. Our alarm went off in the office and everybody escaped out the back door at the fire escape into the alley. I went and tried to shut windows and make sure that everybody was out and OK. There was debris and smoke throughout the entire office.

CUOMO: When you went back up, another detail that really brings home what this was and your proximity to it, what did you find when you went back up?

FOGELMAN: It looked like a gunshot had gone into the window but it didn't go through. Hearing later that there were --

CUOMO: They believe there were ball bearings within the explosive. You know, this sounds like a silly question. You know there was nothing like that in the window before?

FOGELMAN: Yes, the windows were fine before.

CUOMO: And we are hearing that these types of things could have been picked up and around gone through and nobody was hurt though, right?

FOGELMAN: Nobody was hurt, thank goodness.

CUOMO: When you're in your building and you're hearing the explosions, what else are you hearing? What was the atmosphere of some people suffering below?

FOGELMAN: Complete chaos. I mean, we looked out the windows and emergency responders and police officers trying to take care of people as best they could. It was gruesome.

CUOMO: We have been talking tonight about how whoever did this knew the right place and time. What was the density of people on this day outside your building at that point during the day? How thick was it?

FOGELMAN: This one block is probably one of the thickest blocks of the entire marathon stretch. When I walked around 8:30 this morning, people had already lined up. It's also very tight because they built the barricades so there's not a lot of sidewalk space. It's -- this is the block. You're going to do it. CUOMO: That's something that takes a little savvy, right, to know where it's think. You have to know the marathon. You have to know how it works and you have to know a little about timing. That four-hour mark is when you get a bulk of people coming through, right?

FOGELMAN: That's right. The elite runners are through, the wheelchairs are through and all the people who are running for charity that's when they're coming through.

CUOMO: Hopefully next year, the tradition gets back to what it's supposed to be. You'll remember this for how people made it through as opposed to what happened today. I'm glad everybody is all right.

FOGELMAN: Thank you.

CUOMO: Piers, back to you.

MORGAN: Chris, so many of stories of spirit and determination and courage are coming out of Boston. What do you think will happen in the next few days?

CUOMO: Well, I think first of all you are going to have massive investigative capabilities here. You will have multiple federal agencies coordinating with state. The things that we heard yesterday earlier that you were going through about executing a warrant on a particular apartment.

You will hear about a lot of that. There is a lot to go through on a situation where you have such a massively populated event with multiple explosives and no warning, nobody taking credit for it.

Life is going change here in the near term as we see in all these places, Piers, but there is resilience. There is fabric. There is history. There is culture especially in a place like Boston.

Life gets back to normal, but never the same. It gets back to normal but never the same because people will carry this with them. Maybe not in paranoia, we hope, but in a little bit of recognition, this marathon will have a solemnity attached to it that it has never had before but life will go on here in a city like this.

What you hope is that people learn to care about the good moments a little bit more and not just dwell on the bad ones.

MORGAN: So true. Chris for now, thanks very much. We'll be back to you later in the show. When we come back, former Boston Police Commissioner Bill Bratton, what he thinks the investigation could lead.

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MORGAN: We go straight to Chris Cuomo who is live in Boston. Chris, bring us up to date on exactly what we know as a result of what happened this afternoon in Boston. CUOMO: Well, Piers, we know there were two explosions. We know we believe they were coordinated, which means obviously they were not random and they were done as part of the same violent event.

We know they are believed not to be high explosive but low explosive and that provides a window into the nature of sophistication here, getting black powder, low sophistication explosives, easier to do.

Now, that could cut two ways. One means it's a less sophisticated person who did it. But also it could be somebody who knew given the location and the timing of these explosions, the thickest part of the marathon at the time when the most are coming through, where they knew they didn't need more than that.

As a rule of thumb, the less sophisticated the device, the more you have. So when you have multiple bombs, they tend to be less sophisticated. We know that the authorities were aware of all of this. We know the authorities believed they understand how they were detonated.

It was very important if it was done by somebody right next to them or if was remotely or by cell phone. That's why we understand that the investigators are taking a close look at cell tower information to figure out if they can get communications from earlier in the day. That's why they're looking at closed caption TV.

Now this is a huge task. It is reminiscent of 9/11 and as much as you have so many people and so many capabilities and nobody taking credit for it. It creates a thicker investigation.

When you move around this area right now there is a six block perimeter. You have 12 hour shifts with local police with National Guard. You see different vehicles walking around from the federal authorities. There are abandoned strollers, bags, sneakers.

All of them are things that need to be looked at given the nature of this event and it's taking a lot of time, Piers. They have a lot of manpower on the ground here and they are taking it very seriously.

MORGAN: Chris, thank you. Few people know the challenges of trying to safeguard a city like Boston like my next guest. Joining me on the phone is Bill Bratton, the former police commissioner in Boston as well as New York and Los Angeles.

Commission, what do you make of what's happened today. An absolutely appalling event obviously, but do your instincts tell you anything about where the investigation may lead?

BILL BRATTON, FORMER BOSTON POLICE COMMISSIONER (via telephone): Not at this stage. I don't think anybody really knows where it may lead other than the capabilities of the agencies involved. It was truly a horrific day and a day of great tragedy and also watching the videos, some of the runners, the emergency people rushing toward the event.

Some playing understandably but very quickly moving to help those who were injured. Having stood down that rout many times, it was very poignant for me and this brought back any memories of many times. It was just very, very tragic to watch it all.

MORGAN: Is this kind of incident the worst nightmare for any big American city?

BRATTON: Certainly. Every city has major events and every time you have one, for the potential of terrorism event like what occurred in Boston. But, you always hope for the best but expect the worse. Yesterday in Boston, the worse occurred.

MORGAN: There is a marathon over the weekend in Salt Lake City and the London marathon. I'm sure they will be casting anxious glances of what happened in Boston and wonder if they should cancel the events or completely review all security. What would your advice be to them having been through many incidents yourself?

BRATTON: They will go forward. It is a security nightmare with all the passions that she brought to the surface during her life. That will go forward. Baseball games in America are going to go forward. Marathon in Salt Lake will go forward. That's what we do. Can't let the tourists win. All of us will go on like New Orleans.

do you believe -- I understand that we just don't know who caused all of this? Do you believe that the type of operation and the planning it required and the precision of the execution, does it have the hallmarks of an al Qaeda operation to you?

BRATTON: Certainly, al Qaeda likes big events and they like multiple explosions. That has been their hallmark. Was this an al Qaeda event, the investigation will ultimately determine that, but quite clearly -- spectacular event, what better place to pull off something like this when all the eyes of the world are on it.

The irony here is if this event occurred two hours, it would have had hundreds of cameras directly looking down on the scene where those bombs went off. But occurring four hours into the marathon, most of the cameras were gone.

Most of the video that I have been watching is amateur video. It's unprofessional video because by that time, all the professional cameras had left. The crowds had thinned down quite a bit from what they were.

MORGAN: Commission, Chris Cuomo is live for CNN in Boston. I think he has a question for you now -- Chris.

CUOMO: Commission, good to hear your voice. Let me ask you something. We are talking about the staging of this event. Two factors that I would like you to put into context in terms of what they could mean.

One, insider knowledge of understanding that this corner would be thick with people and this time just over four hours into the marathon would be the right time to have the thickest group come through.

And the idea that local cops had done sweeps of this particular area not long before, which might suggest that whoever did this was nearby, how do those factor in?

BRATTON: The idea it's four hours into the race. I have worked that marathon probably 20 times in my career. There is still as you see clearly in the video, large numbers of people and large numbers of runners. By that time, however, most of the national and international media had stopped filming that race because the race for their purposes was over.

What you now had was people that 20,000 runners probably about six hours to get the bulk of them in. The timing of it, quite frankly, was a little odd. It might have taken advantage of the fact that security might have lessened somewhat in terms of the area. That's something that they will take a look at minute by minute what was going on there.

CUOMO: Commissioner, thank you. You'll be proud of your people here -- the civilians also are doing their best.

BRATTON: Watching those videos from yesterday, it was phenomenal the heroism, people running towards the explosions, many others running towards it.

MORGAN: Pretty amazing. Chris Cuomo, thank you very much. I'm going to leave you now. Also, thank you to Commissioner Bill Bratton for that great insight, a great Boston man paying tribute to the great acts of heroism that so many showed today amid the tragedy.

Many amazing stories are coming out of the Boston marathon disaster. One of them is this one, a 78-year-old elite runner, thrown to the ground by the first explosion. Watch as the moment is captured.

(BEGIN VIDEOTAPE)

MORGAN: The whole world has seen the images of you being blown off of your feet. Tell me exactly what you experienced as you ran towards the finishing line?

BILL IFFRIG, 78-YEAR-OLD RUNNER WAS KNOCKED TO GROUND: I was approaching the last straight away to the finish line and I had had a good day and I was feeling really good. I got down to within about 15 feet of the finishing apron and this tremendous explosion, shock waves hit my whole body and my legs jittered around.

I knew I was going down so I ended up down on the black top. I didn't feel any severe pain, but as I rolled over I seen a little scratch on my leg so I laid there just momentarily. One of the finisher assistants talked to me and asked if there is anything they needed to do and offered to give me a hand and offered to help me get up and over the finish line so I could complete my race.

We did that and I felt OK. Before they had one rounded up, I think I can make it OK. They let me get out of there and I went on home to my wife.

MORGAN: Extraordinary that you would finish the race. I think this was your third Boston Marathon. When you got back to your hotel and began to realize the scale of the disaster that unfold what was your reaction?

IFFRIG: Well, I guess I mulled it over by then I didn't know what was going on. I wondered if it might be a terrorist plot and that doesn't happen every day. As far as the way I was feeling, it felt pretty good.

MORGAN: Have you been aware that your pictures are seen around the world?

IFFRIG: I have had a lot of contacts here, yes. Since today you mean?

MORGAN: I want to bring in Bill, if I may, the photographer that took the picture of you. They are still images that have gone around the world. His name is John Mackie. John, would you like to talk to Bill and tell him what you saw?

UNIDENTIFIED MALE: I just -- I feel bad for Bill that he couldn't enjoy his marathon finish. I mean, what a way to end a marathon with a bomb blast. I think of all the thousands of people who come to the Boston Marathon every year.

And especially like Bill who, you know, this is -- this is a Boston treasure. I'm just so saddened by what happened. My images are haunting to me and everybody else. It's just too bad they could not be the regular joyous, celebratory images that I take all the time for the "Globe."

MORGAN: Bill, it is awfully heartbreaking that such a joyous event, one of Boston's great days of the year has turned into such a terrible atrocity today. What are your feelings about the people or the person that perpetrated this act?

IFFRIG: I thought about that myself. Everybody else is out there having fun and you have one or two people trying to destroy the whole thing and it's hard to figure out. Terrorists or whatever they are. I don't know.

MORGAN: Will you continue to run marathons after this?

IFFRIG: Yeah, yes. I don't stop for this.

MORGAN: Do you think that should be the attitude of everyone in America to what has happened?

MORGAN: A remarkable man with a remarkable spirit. When we come back, what would it take to keep Americans safe at events like marathons? I'll ask an expert.

(COMMERCIAL BREAK)

MORGAN: In the wake of a terror attack, the Boston Bruins and Celtics game, and Pacers game originally scheduled for Tuesday was also cancelled. Joining me now is Dan Donovan, a crisis management consultant. He works in Atlantic Olympics bombing in 1996 and with me in New York is Paul Cruickshank.

Before I come to you, Dan, I want to ask Paul Cruickshank, what was your reaction to Bill Bratton's assessment of what went on today?

CRUICKSHANK: Well, it was an interesting assessment and one of the big questions of who was responsible. These devices appear to have been quite rudimentary. They were not huge bombs. Did they get a lot of training? It doesn't seem to be the case.

MORGAN: Dan, sporting fixtures already being cancelled in the wake of this, probably more out of respect than anything else. But going forward this is going to change the way that America puts on big sporting events for quite a while won't it?

DAN DONOVAN, SPORTS AND ENTERTAINMENT GUIDEPOST SOLUTIONS: Today's events, specifically tonight's games with the Celtics and Bruins, we have two issues. Is it safe to play tonight? Is it the right thing to do and do you have the resources to keep any open course safe?

You have is it the right thing to do from a public perception. That's today's issues and going forward there are a number of topics that have to get addressed. Each league and event owners are going to address it to the best of their ability.

Do we have the resources financially to protect the events the way we would like to in every instance and we know we don't.

MORGAN: When you have this volume of people, I'm thinking ahead to the fall when you have the New York marathon, another huge potential target. It's obviously their worst nightmare come true that kind of incident.

DONOVAN: In a city like New York to put on a marathon there's going to be a lot of planning to take place and probably a lot of technologies, a lot of sharing of information.

That intelligence community is going to be hard at work to make sure that any possible indication that they may have a threat or increased risk, they're going to address accordingly.

But these open events like marathons, road races, triathlons, the America's cup coming to San Francisco soon. We just had golf in Augusta, very difficult events when they're this wide open.

MORGAN: Don, thank you very much. Paul, if you put all the pieces together of this, it does have the hallmarks of an al Qaeda style attack in the sense of clearly premeditated, well planned, well executed, maximum publicity at the big event.

You could also argue that it's the hallmark of a lone wolf given the type of devices that are being used. I don't think at this stage of where we have a real idea either way.

CRUICKSHANK: It could be al Qaeda. It could be al Qaeda inspired or it might be nothing to do with Islamic terrorism at all. It may be a lone wolf. We saw in Norway a year or so ago with a significant terror attack carried out by one person. So many, many questions at this hour appear. Whoever is responsible for this seems to be still at large and has the capability to make these bombs. That will be causing a lot of concern.

MORGAN: It would be very, very keen to catch whoever it is. That's for sure. Paul Cruickshank, thank you very much.

Many are questioning the future of the Boston marathon in global event forever change by tragedy. Professional running coach, Fred Treseler has trained more than 3,000 people to run the race.

Mr. Treseler, thank you for joining me. It's an awful day for you and everyone who loves the Boston marathon, what is your reaction to what's happened?

FRED TRESELER, FOUNDER AND PRESIDENT, TRACS: It is a terrible day for the city of Boston, for the commonwealth of Massachusetts, for our country, and for the sport of running globally. It's just a terrible blow.

And it's really just we're all in a situation where the tragedy, the loss of life that has already been reported, the injuries has created kind of a shock, if you will, that has certainly permeated all parts of our community.

What we do know at this moment, Piers, is we have heard lots of different statistics about how many injured. Here is what we do know and I'm happy to share with you. That 23,326 people officially started the race this morning.

At 17,584 crossed the finish line, 4,496 made it to the 40-kilometer mark, but are unaccounted for because they were held up from coming into the square area and to properly cross the finish line. Another 1,246 never made it to the 40-kilometer mark.

So the good news is that 17,584 got across the finish line safely that the BAA and Boston police did a fantastic job. I worked with the elite athlete program in the past. They have tremendous plans in place for something like this.

And the way that the race was suspended so quickly and how they so quickly kept people from coming down the street where they could be at risk or danger was absolutely fantastic. And I think the Boston Athletic Association and the Boston police and the state police deserve tremendous credit for how they handled this when it occurred.

MORGAN: They certainly do and probably saved a lot more death and injuries as a result of their rapid actions. To me, the guy that sums up was a man earlier, 78 years old. He has run 45 marathons and blown off of his feet. He just got back up and finished the race. What did you make of that, Fred? TRESELER: You know I think he speaks a lot to the spirit of the marathon and the connection that so many people to this particular run and this particular distance. You know, I feel terrible for the people who have been injured in this senseless attack.

But I also feel for the thousands of people who trained for months who raised money for charities. And all of a sudden they can't get to the finish line or that they are experiencing crossing the finish line is marred by this terrible tragedy.

Think about it. For the one from Kenya or Denissa from Ethiopia, tomorrow would have been the day that they would have been heralded in our newspapers. Tomorrow, it will be about this local tragedy. And those two athletes have been robbed as well of their moment in history by this terrible thing.

MORGAN: Finally, will there be a Boston marathon next year?

TRESELER: The Boston Marathon has endured two world wars and many other things. I remember working with the elite athlete program after September 11 and the different things that were put in place to deal with that. I am quite sure that there will be a Boston marathon next year, but for certain, the Boston marathon has been changed forever.

MORGAN: It certainly has. Thank you so much for joining me.

TRESELER: You are welcome and please to all of your viewers, please share your thoughts and prayers with those in Boston tonight.